High-power Y-junction H-plane circulator for microwave transmission

ABSTRACT

A circulator for the transmission of microwave energy comprises three coplanar waveguides of rectangular cross-section forming a Y-junction in their magnetic plane. Two heavy metal discs parallel to that plane are secured at that junction to opposite inner wall surfaces of the circulator and in turn support a pair of ferrite pellets spacedly confronting each other. A pair of permanent magnets on the outer circulator surfaces, coaxial with the pellets and discs, generate between the pellets a strong magnetic field which saturates the pellets and approaches a limiting value of about 3,000 oersteds beyond which first-order non-linear effects are negligible, this field strength being less than the gyromagnetic-resonance field but greater than that which minimizes the critical power in the circulator.

United States Patent Lahmi et al.

[ July 15,1975

[ HIGH-POWER Y-JUNCTION II-PLANE CIRCULATOR FOR MICROWAVE TRANSMISSION [75] Inventors: Henri Lahmi; Alain LaGrange, both of Paris, France 73] Assignee: Thomson-CSF, Paris, France [22] Filed: Nov. I4, 1973 [2i] Appl No.: 415,751

[30] Foreign Application Priority Data Nov. I7, 1972 France 40897 [52] US. Cl. 333/1.1; 333/98 R [51] Int. Cl.

[58] Field of Search 333/1.l, 24.1

[ 56] References Cited UNITED STATES PATENTS 3 l04,36l 9/1963 Leetmaa et al. 333/l.l

Primary ExaminerPaul L. Gensler Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT A circulator for the transmission of microwave energy comprises three coplanar waveguides of rectangular cross-section forming a Y-junction in their magnetic plane. Two heavy metal discs parallel to that plane are secured at that junction to opposite inner wall surfaces of the circulator and in turn support a pair of ferrite pellets spacedly confronting each other. A pair of permanent magnets on the outer circulator surfaces, coaxial with the pellets and discs, generate between the pellets a strong magnetic field which saturates the pellets and approaches a limiting value of about 3,000 oersteds beyond which first-order non-linear effects are negligible, this field strength being less than the gyromagnetic-resonance field but greater than that which minimizes the critical power in the circulator.

8 Claims, 5 Drawing Figures 1060 who 1 HIGH-POWER Y-JUNCTION H-PLANE CIRCULATOR FOR MICROWAVE TRANSMISSION The present invention relates to highpower. Y- junction. H-plane circulators for the transmission of microwave energy in a temperature range between 40 C and 85 C.

Those skilled in the art will be aware that a Y- junction circulator is a passive transmission device comprising at least three channels arranged in the same plane. converging towards the center of the device. Devices of this kind do not satisfy the reciprocity principle. that is to say that a wave entering through a chan nel selected as the input channel is transmitted substantially wholly to one of the adjacent channels. referred to then as the coupled channel and chosen as the output channel. whereas it is not transmitted at all. or at any rate only in a very highly attenuated form. to another channel which is known as the decoupled channel. At the center of the circulator there are one or more components generally constituted by a ferromagnetic material saturated by a direct magnetic bias field referred to as the static field. which is fundamentally the cause of this phenomenon.

Circulators are utilized in order to deliver to an antenna. e.g. from a transmitter of the radar type. signals constituted by pulses of very high power level. separated by time intervals which are much longer than the duration of each pulse. On the other hand. the circulator has to feed to a receiver the pulses picked up by the antenna. The problem of high-power transmission then takes on a dual aspect:

as far as the mean power is concerned. this is limited by the magnetic losses of the saturated material; in other words. these losses produce heating of the material. generally resulting in deterioration of its ferromagnetic properties and. consequently. in deterioration of the transmission characteristics of the circulator:

as far as the peak power is concerned. this must not reach a critical level beyond which transmission is influenced by non-linear phenomena which affect the transmission performance of the circulator.

Devices are known. more or less close to junction circulators proper. which are capable of circulating energy at high mean and peak power levels between different coupled and decoupled channels but these devices exhibit a variety of drawbacks. In particular. differential phase-shift circulators make it possible, for ex ample. to transmit a mean power of several kW and a peak power of the order of l kW. but they are much heavier and more bulky than junction circulators of like power-transmitting capacity. Thus. for example, the respective weights of X-band circulators of these two types are kg and 200 g, and the costs are likewise rectangular cross-section forming a Y-junction in their magnetic plane. a pair of ferromagnetic elements with faces parallel to that plane spacedly confronting each other within that junction and lying in a constant magnetic biasing field perpendicular to these faces. The field. generated by a source of unidirectional magnetic flux such as a pair of permanent magnets on the outer surfaces of the waveguide structure. is of a magnitude below the gyromagnetic-resonance point but above the minimum-critical-power point of the circulator. approaching a limiting value beyond which first-order non-linear effects are negligible. As more fully discussed hereinafter. this limiting value H, is generally close to 3.000 oersteds.

According to a more particular feature of our invem tion. the ferromagnetic elements are ferrite pellets secured to opposite inner wall surfaces of the waveguide structure through the intermediary of a pair of heavy metal discs coaxial with these pellets but of larger diameter. The permanent magnets generating the biasing field can be circular and coaxial with the pellets.

The limiting field H, satisfies the relationship:

where H, is in oersteds. F is the mean operating frequency of the circulator in Mes. N is the demagnetization factor in the direction of the static field. and 411'M. is the saturation magnetization in C.G.S. units.

The invention will be better understood and other of its features will become apparent from the ensuing description given with reference to the attached drawing in which:

FIGS. l and 2 are explanatory graphs pertaining to physical phenomena upon which the invention is based:

FIGS. 3 and 4 are horizontal and vertical sections through a circulator in accordance with the invention. associated with rectangular waveguides having walls parallel to an applied magnetic field (H) the section of FIG. 4 being taken on the line IV-IV of FIG. 3'. and

FIG. 5 illustrates another embodiment of the invention.

In FIG. 1 we have plotted on the abscissa axis OP the instantaneous power in watts of a short-wavelength electromagnetic oscillation (X-band for example) injected into an input channel of a Y-junction. H-plane circulator whose bias field can be varied. On the ordinate axis 0A. the attenuation in dB. measured between the input channel and the output of a coupled channel of this circulator. has been plotted. For the usual staticfield strengths, for example 1.500 oersteds. and an operating frequency of 10 Gcs. a graph would be obtained comprising two sections I and II meeting at a point P.. whose abscissa is the aforementioned critical power. Below the critical-power point P. the attenuation is substantially constant (section I). whereas above that point the attenuation rises rapidly with input power (section II). It will be observed that if a greatly increased bias field is applied. for example on the order of 3000 oersteds. the matching conditions of the circulator being modified accordingly. the corresponding graph extends at the high-power side in the form of a section III which is substantially parallel to the abscissa axis. In other words. at high static field strengths there is no critical power: the limitation is no longer determined by non-linear effects in the ferromagnetic material.

Within the scope of the invention we have determined. for various static-field strengths, the behavior of a circulator in which the saturated ferromagnetic medium is a ferrite material. for example an yttrium and gadolinium garnet having a narrow spin-wave linewidth and a magnetic moment below 1300 CGS units on the order of 1200 CGS units, were studied.

In FIG. 2, a graph plotting the critical power P,. as a function of the static-field strength H has been shown. This graph has a minimum M at H H and P,.= P and an asymptote parallel to the ordinate for the value H H already defined. For example, for a junction circulator designed to operate on the X-band, we have found that this power P is on the order of 20 kW for 1000 oersteds and on the order of 10 kW for 2200 oersteds, rising to 200 kW for 2600 oersteds.

The equation of the asymptote is H H (on the order of 2800 oersteds). It will be seen, therefore, that with a bias field H substantially in excess of H and close to the limiting field strength H, a critical power of several hundred kW is obtained. The circulator shown in FIGS. 3 and 4 is of the ternary-junction kind cooperating with X-band rectangular waveguides in a plane parallel to the longer sides of the waveguide section (H-plane).

FIG. 3 is a central-section through this H-plane, FIG. 4 being a section in a plane perpendicular thereto. The junction J, with three coplanar rectangular waveguides G G and G spaced 120 apart, is equipped with two thick metal discs ll reducing the internal height of the waveguides at the location of the junction. Onto the free faces of each of disc, and at the center thereof, there have been pasted two ferrite pellets 12 of smaller diameter than the discs and having thicknesses of the same order as she the optimum dimensions of the discs and the pellets can be determined experimentally, the value H of the biasfield strength being kept fixed, whereas in conventional technology the value of the bias-field strength is used to adjust the operation of the circulator. The field strength H of the order of 2800 oersteds is created by two cylindrical magnets 13 located at either side of the junction .1 and provided with flat faces parallel to the larger faces of the discs and pellets.

FIG. 5 illustrates an embodiment of the invention, wherein the circulator comprises a ternary junction of the type known as T-type, i.e. a Y-junction modified as follows: the waveguides G. and G similar to those of FIG. 3, comprise a first portion G or G disposed 120 apart and at 120 on either side of the waveguide G3. they further comprise, commencing at a certain distance from the junction, a second or output portion G or G extending at 90 to the waveguide G so that the output portions G and G are collinear. The two portions of waveguides G and G are linked by curved intermediate sections.

The dimensions of the circulator shown in FIG. 5 are as follows:

internal section of the waveguides: 22.86 mm X discs 11: diameter 31.4 mm; thickness 1.95 mm;

pellets 12: diameter mm; thickness 2.2 mm:

magnets 13: diameter 14 mm; thickness 7 mm.

The materials employed are as follows:

Waveguides: light aluminum alloy;

discs I 1: aluminum alloy;

magnets 13: samarium and cobalt permanent magnet developing between the pellets 12 field strength of oersteds in the cases (a) and (b) mentioned hereinafter:

pellets I2-case (a): garnet ferrite of the overall formula:

Y Gd Fe 0 where x 0.3 t 10 whose characteristics are as follows at ambient temperature:

Saturation magnetic moment: 1230 U.C.G.S.

Resonance linewidth at 9.5 Ge: oersteds;

Gyromagnetic factor: 2.01

Relative dielectric constant (at 9.5 Gc): 15.5

Tangent of dielectric-loss angle (at 9.5 Gc): 2.10

Curie point: 280 C Spin-wave linewidth at 9.5 Gc: 6.5 oersteds case (b): garnet ferrite of the overall formula:

Y Fe A1 0, where y 0.074 1 10 percent whose characteristics at ambient temperature are as follows:

Saturation magnetic moment: I200 U.C.G.S.

Resonance linewidth at 9.5 Ge: 40 oersteds Gyromagnetic factor: 2.01

Dielectric constant at 9.5 Gc: 14.8

Tangent of dielectric-loss angle at 9.5 Go: 2.10

Curie point: 225 C Spin-wave linewidth at 9.5 Gc: 2.9 oersteds.

The circulator exhibits the following characteristics:

Frequency band: 8.5 to 96 Ge Operating temperature range: -40 to C Maximum insertion losses: case (a): 0.5 dB; case (b):

Decoupling between channels: 20 dB Maximum standing-wave ratio: 1.30

Permissible peak power: kW at standing-wave ratio of 1.8; 200 kW across matched load.

Permissible mean power: 1 10 Watts at standing-wave ratio of 1.8; 200 Watts across matched load.

Apart from the junction circulators described and illustrated, the invention is applicable to any device which does not satisfy the reciprocity principle thanks to the use of a ferromagnetic material saturated by a steady biasing field.

The invention is applicable to the manufacture of other microwave devices such as non-reciprocal phaseshift devices, duplexers, etc, in particular in the case of transmission equipment intended for installation in aircraft or airborne equipment.

What we claim is:

I. A circulator for the transmission of microwave energy, comprising:

a metallic structure including three coplanar waveguides of rectangular cross-section forming a Y- junction in their magnetic plane;

a pair of ferromagnetic elements with faces parallel to said plane spacedly confronting each other within said Y-junction; and

a source of unidirectional magnetic flux generating between said faces a constant magnetic biasing field perpendicular to said plane saturating said ferromagnetic elements, said field having a magnitude below the gyromagnetic-resonance point but above the minimum-critical-power point of the circulator 6 and approaching a limiting value beyond which source comprises a pair of permanent magnets first-order non-linear effects are negligible. mounted on opposite outer surfaces of said structure in 2. A circulator as defined in claim 1 wherein said limcoaxial relationship with said pellets and discs. iting value is on the order of 2,800 oersteds and said 6. A circulator as defined in claim 5, wherein said minimum-critical-power point is about 2,200 oersteds, 5 pellets consist of a garnet ferrite. said magnitude being close to said limiting value. 7. A circulator as defined in claim 6, wherein said 3. A circulator as defined in claim 1, further comprisgarnet ferrite is of the general chemical formula:

ing a pair of metallic discs secured at said Y-junction to opposite inner surfaces of said structure, said ferro- (3-3 where x i percent magnetic elements being supported on said discs. m 8. A circulator as defined in claim 6, wherein said 4. A circulator as defined in claim 3 wherein said fergarnet ferrite is of the general chemical formula: romagnetic elements are ferrite pellets coaxial with Said discs. a s-su a 12 Where J 0-074 i 10 P 5. A circulator as defined in claim 4 wherein said 

1. A circulator for the transmission of microwave energy, comprising: a metallic structure including three coplanar waveguides of rectangular cross-section forming a Y-junction in their magnetic plane; a pair of ferromagnetic elements with faces parallel to said plane spacedly confronting each other within said Y-junction; and a source of unidirectional magnetic flux generating between said faces a constant magnetic biasing field perpendicular to said plane saturating said ferromagnetic elements, said field having a magnitude below the gyromagnetic-resonance point but above the minimum-critical-power point of the circulator and approaching a limiting value beyond which first-order nonlinear effects are negligible.
 2. A circulator as defined in claim 1 wherein said limiting value is on the order of 2,800 oersteds and said minimum-critical-power point is about 2,200 oersteds, said magnitude being close to said limiting value.
 3. A circulator as defined in claim 1, further comprising a pair of metallic discs secured at said Y-junction to opposite inner surfaces of said structure, said ferromagnetic elements being supported on said discs.
 4. A circulator as defined in claim 3 wherein said ferromagnetic elements are ferrite pellets coaxial with said discs.
 5. A circulator as defined in claim 4 wherein said source comprises a pair of permanent magnets mounted on opposite outer surfaces of said structure in coaxial relationship witH said pellets and discs.
 6. A circulator as defined in claim 5, wherein said pellets consist of a garnet ferrite.
 7. A circulator as defined in claim 6, wherein said garnet ferrite is of the general chemical formula: Y3 3x Gd3x Fe5 O12 where x 0.3 + or - 10 percent.
 8. A circulator as defined in claim 6, wherein said garnet ferrite is of the general chemical formula: Y3 Fe5 5y Al5y O12 where y 0.074 + or - 10 percent. 